The two dams, Bennett and Peace, together generate 40% of British Columbia's hydroelectricity, much of it exported to the United States. The rate of electric generation here in summer is closely tied to the temperature in southwestern cities such as Los Angeles and Phoenix — when the air conditioners go on the electricity demand goes up. In winter it is the opposite, and power flows north to heat Canada (many of whose rivers are frozen). The Peace River Project is the northern end of the Pacific Intertie, a colossal system of high voltage power lines that tie together all the major power grids of western North America, from here to San Diego.